1. Field of the Invention
The present invention to a developing device adapted for use in, for example, an electrophotographic copying machine, and more specifically to a developing device for developing a latent image by means of a one-component developing agent.
2. Description of the Prior Art
Recently, developing devices have been proposed for electrophotographic copying machines which use a one-component developing agent containing no carrier for development. FIG. 1 shows one such prior art developing device. In FIG. 1, a developing roller 16, as a developing agent carrying means, is disposed opposite a developing agent feeding outlet 14 of a developing agent hopper (toner hopper) 12 which stores a developing agent 10 therein. A charging blade 18 and a recovery blade (seal blade) 20 are attached to the upper and lower edge portions of the developing agent feeding outlet 14, respectively. The respective distal end portions of the two blades 18 and 20 are pressed against the outer peripheral surface of the developing roller 16 so that the developing agent feeding outlet 14 is closed by the developing roller 16 and the blades 18 and 20. The developing agent 10 in the developing agent hopper 12 stirred by a stirring member 22 is delivered as the developing roller 16 rotates. The delivered developing agent 10 is charged and formed into a thin layer by the charging blade 18. The charged developing agent 10 serves to develop an electrostatic latent image which is previously formed on a photoconductive drum 24 as an image carrier.
An untransferred portion 10' of the developing agent 10, having passed through a developing region D where the photoconductive drum 24 and the developing roller 16 are nearest to each other, still remains on the developing roller 16 by the agency of a reflected image force. As the developing roller 16 rotates, the developing agent portion 10' is conveyed and re-collected into the developing agent hopper 12, passing by the recovery blade 20.
In the conventional developing device of this type, however, the distal end of the recovery blade 20 extends toward the charging blade 18 so that the recovery blade 20 covers the top surface portion of the developing roller 16 which faces the developing agent feeding outlet 14. In other words, the distal end of the recovery blade 20 is buried in the developing agent 10 stored in the developing agent hopper 12. Accordingly, a developing agent feed zone A or that portion of the outer peripheral surface of the developing roller 16 which is in contact with the developing agent 10 in the developing agent hopper 12 is narrow. Thus, if the developing roller 16 is reduced in diameter, it will not be able to be satisfactorily supplied with the developing agent 10.
In the prior art developing device constructed in this manner, the distal end of the recovery blade 20 is located in the developing agent 10, as mentioned before. Therefore, that portion of the developing agent 10 which is in contact with that surface of the recovery blade 20 on the side (reverse side) not in contact with the developing roller 16 is prevented from being supplied to the developing roller 16 by the recovery blade 20. Thus, dead space B of a substantial size is produced at the back of the recovery blade 20, resulting in a waste of the developing agent 10.